Every year, the German CTF Team "Eat Sleep Pwn Repeat" sets out to organize the C3 CTF.
We always try to come up with new and novel challenges which are related to real life things you may encounter as a hacker:
Browsers, Hypervisors, Operating Systems, Mobile phones etc.
Andy always wanted to build a proper GSM based mobile phone as part of such a challenge.
Thanks to the osmocom project which provided all the necessary protocol stack implementations, this was finally possible.
This talk will guide you through how GSM works, how he built the phone and what the bugs were he planted in the challenge for the teams to find and exploit.